The field of the invention is polyamide adhesives for textiles and the present invention is particularly concerned with heat sealing textiles with copolyamides.
The state of the art of copolyamides used in the heat sealing of textiles may be ascertained by reference to U.S. Pat. Nos. 2,252,555; 3,515,702; 3,839,121; 3,883,485; 3,883,487; 3,948,844; 3,950,297; and 4,368,090, as well as West German Published Applications Nos. 2,436,430; 2,508,112; 2,642,244; 2,806,933; and 3,005,939, the disclosures of which are incorporated herein by reference.
The use of copolyamides as thermoplastic adhesives has long been known and U.S. Pat. No. 2,252,555 is an illustration of an early use. Lauryllactam based thermoplastic adhesives have been used recently in the technique of heat sealing textiles as disclosed in U.S. Pat. No. 3,515,702. These thermoplastic adhesives sometimes fall short in performance, particularly regarding hot water resistance. They have been modified in many ways to avoid these short falls.
Thus, U.S. Pat. No. 3,839,121 discloses thermoplastic adhesives based on copolyamides appropriately containing branched chain diamine components which give improved resistance to washing solutions. West German Application No. 3,005,939 also discloses copolyamides containing singly branched C.sub.10 -diamines such as 5-methylnonamethylene diamine. These copolyamides are also recommended as textile thermoplastic adhesives. They evince fairly good resistance to hot water but must be fixed at higher temperatures. Nonamethylene diamine based copolyamides also have too high a melting point and, therefore, are unsuitable as thermoplastic adhesives for heat sealing textiles and these copolyamides are disclosed in West German Applications Nos. 2,508,112 and 2,642,244. Copolyamides of low melting points are unsatisfactory with regard to their resistance to hot water and to cleaning and they are disclosed in West German Applications Nos. 2,436,430 and 2,806,993, and U.S. Pat. Nos. 3,883,485; 3,950,297; 3,883,487, and 3,948,844.
In most cases textiles are finished, that is provided with a coating, whereby they get a better feel or are made water-repellent. They are made water-repellent for instance by being siliconized. The thermoplastic adhesives of the prior art are inadequately effective for silicon finished textiles. In other words, the adhesive does not bond silicon finished textiles well enough.
A substantially improved thermoplastic adhesive to bond siliconized fabrics is disclosed in U.S. Application Ser. No. 388,427, filed July 14, 1982, and now abandoned. This thermoplastic adhesive is used in a powder form to heat seal textiles and consists of a mixture of specific proportions of selected copolyamides of higher and lower melting points.
Besides the fact that this thermoplastic adhesive is especially effective only when used in its powder form, it also requires substantial application of specialized apparatus to prepare the mixtures according to the particular formulations. Lastly, these thermoplastic adhesives of the state of the art still require improvement.